Integrated circuits typically include a large number of components, particularly transistors. One type of transistor is a metal-oxide-semiconductor field-effect-transistor (MOSFET). MOSFET devices typically include a gate structure on top of a semiconductor substrate. Both sides of the gate structure are doped to form source and drain regions. A channel is formed between the source and drain regions beneath the gate. Based on a voltage bias applied to the gate, electric current may either be allowed to flow through the channel or be inhibited from doing so.
In some cases, the channel may be formed as a fin-like structure (herein “fin”). Such a fin protrudes beyond a top surface of the substrate and runs perpendicular to the gate structure formed on the substrate and the fin. Typically, a gate dielectric layer (e.g., an oxide layer) is formed between the fin and the gate structure so as to allow the gate structure to provide optimal control over the electric current flowing through the channel.
A variety of thermal oxidation, vapor deposition (e.g., chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), etc.), and/or layer deposition (e.g., atomic layer deposition (ALD), plasma-enhanced layer deposition (PLD), etc.) techniques are used to form such an oxide layer. Forming an oxide layer with a conformal thickness over the fin (e.g., the channel) is generally a goal to pursue. The thermal oxidation techniques may encounter some issues to reach such a goal due to different crystal orientations of sidewall and top surface of the fin, respectively. Although the vapor and/or layer deposition techniques may be able to form a conformal oxide layer, the oxide layer may have a poor insulation quality. Accordingly, one or more post annealing processes are generally needed to cure the oxide layer. However, this post annealing process may cause atom loss (e.g., silicon loss) in the fin channel thereby forming defects, which disadvantageously impacts overall performance of such a fin-based transistor. Thus, conventional techniques to form an oxide layer in fin-based transistors are not entirely satisfactory.